AGN Research with Future Interferometric Arrays

Andreas QuirrenbachLandessternwarte Heidelberg

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The VLT Interferometer

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Optical / Infrared Interferometry Today

Access to milliarcsecond-scale phenomenaPerform interferometric spectroscopySensitivity sufficient for a few bright AGNImportant information on dust distribution from observations in 10µm band (talk Walter Jaffe)

Small number of telescopes ⇒ parametric model fits to visibilities, no imagesSensitivity insufficient for larger samplesResolution insufficient for details / more distant objects

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Desirable Capabilities of a Next-Generation Interferometer

Address wide range of scientific topics ⇒flexibilityObserve faint objects ⇒ high sensitivity and dynamic rangeComplex objects / limited prior knowledge ⇒imaging capabilityAccess “famous” archetypical and rare objects ⇒ good sky coverageObserve time-variable phenomena ⇒ good snap-shot capability

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What’s Next?

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What’s Next?

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Think BIG!

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The ELSA Concept – a Strawman Interferometric Facility

Number of telescopes: 27Telescope diameter: 8 mMaximum baseline: 10 kmWavelength range: 500 nm … 20 µm (?)Beam transport: Single-mode fiber bundlesBeam combination: MichelsonSky coverage at 600 nm: & 10%Cost: ≈ 400 M€

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Linear Resolution of ELSA in the Local Universe

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Linear Resolution of ELSA atλ = 500 nm

Redshift z0 2 4 6

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A Y-Shaped Configuration(15 Telescopes)

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AGN Science with ELSABlack-hole mass from stellar and gas dynamicsReverberation mapping (watch line response to continuum variations in movies) ⇒ physics of BLR, geometric distancesOptical emission from milliarcsecond jets ⇒jet collimation, shocks, particle acceleration, …Details of clumpy (?) obscuring torus ⇒ dust properties, unification schemes“Mirror(s)” in HBLR objects ⇒ AGN physics, unification schemes

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ELSA Critical TechnologiesTelescopesArray co-phasingBeam transportBeam combinationDelay compensation

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ELSA Co-Phasing ConceptPhase individual telescopes with multiple (?) LGS adaptive opticsOff-axis fringe tracking on “bright” starLarge aperture ⇒ good fringe tracking sensitivity ⇒near-complete sky coverageRequirement: fringe tracking at K≈19• One of the drivers for large array elements

Fringe-tracking chain of neighboring telescopes for bright (resolved) starsFringe tracking between all telescopes for faint (unresolved) stars

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Limiting Sensitivity for Fringe Tracking in the R Band

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Sky Coverage at NGP for Different Maximum Off-Axis Angles

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ELSA TelescopesNeed to produce twenty-seven 8m telescopes for ≈ 200 M€Moveable for array reconfiguration if possibleSmall field-of-viewNo scientific instruments (acquisition and fiber-feeds only)Take advantage of ELT development• Mass production of mirror segments• Standardized structural elements

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Projected Cost of TelescopesTypical scaling of telescope cost with diameter is € ∝ D2.7

Scaling applies at any given time (for similar maturity of technology), not to future projectionExample: scaling holds for Keck (10m) versus CHARA (1m) telescopesApply scaling to ELT (e.g., European E-ELT concept): 42m for 700 M€ ⇒ 8m for 8 M€Proof-of-concept for ELT?

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Moving Big Telescopes around …

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… is Perfectly Doable!

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ELSA SiteNeed flat ≈ 10 km plateauGood seeing (r0, τ0, θ0) important criterionSouthern hemisphere preferredRequirements different from ELT criteriaALMA site probably (marginally) ok

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What Needs to be Done?Currently there is no formal “Future Large Interferometer” projectPlanning is beginning now• Detailed science case• Technology development roadmap• Site evaluation

Need to get into “official” facility planning• US: Decadal Review• Europe: ESO, EU, Astronet• Others: ??

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ConclusionsA large interferometer – such as ELSA – will open completely new windows on AGN scienceIt is (almost) doable technically now, but some technology development is needed to bring cost downThe science case needs to worked out in detailPlanning and lobbying is neededInternational cooperation will be helpful to finance an €xtremely £arge $ynthesis Array¥

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Questions to YouWhat angular resolution is needed for your science?What limiting magnitude do you need?What are the imaging requirements (dynamic range, field-of-view etc.)?Is polarimetry needed (technically difficult)?Which scientific topics have I missed?Would you like to help?Please send answers to: A.Quirrenbach@lsw.uni-heidelberg.de